Page 268 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Formation Damage by Inorganic Deposition 239

adsorption or precipitation on the rock surface or other mechanisms.
After the well is placed back on production, the inhibitor slowly dissolves
or desorbs from the rock and enters the produced water and sea water
over time.
As the squeezed chemicals flow back into the well with the produced
fluids, the inhibitors inhibit the formation of scale from the sand face to
the topside facilities. Ideally, the inhibitor will return over a period of
weeks or months at a low concentration just above the minimum inhibi-
tor concentration (MIC) that is required to prevent scaling (Graham
et al., 2005). The MIC is linked to the severity of the scale problem
depending on the ratio of sea water and produced water and the concen-
tration of scaling ions in the formation water. A high MIC could lead to
more frequent treatments. However, the limitations of the methods have
become apparent in more challenging environments such as deepwater or
remote wells because these wells usually require intervention-free and
totally reliable scale-prevention strategies are demanded. Scale inhibitor
treatment frequencies are typically 2 3 per year per well depending on
the volume of produced water treated. Squeeze lifetimes are sometimes
referred to in total barrels of produced water treated. The squeeze life-
time is strongly influenced by the severity of the scaling environment,
inhibitor chemistry, the MIC, and the formation properties. The general
industry experience is that the first squeeze treatments performed on a
well give the shortest lives leading to a higher intervention frequency
during early sea water breakthrough.
Fig. 5.13 shows a typical scale inhibitor squeeze treatment. In the pre-
flush stage, typically of about 50 barrels of flush fluid mixture is injected.
The preflush fluids usually contain some biocide and scale inhibitors up
to 200 ppm. The purpose of a preflush is to maximize the fluid contact
with rock to reduce near wellbore damage. After the preflush, the main
inhibitor treatment will be started with a volume of 250 to 500 barrels
based on the treatment design. Following the main treatment, about 500
barrels or more fluid will be injected to ensure the accurate placement of
chemicals. A typical treatment is usually less than 30 ft from the wellbore,
and the reservoir gross thickness significantly affects the actual volume
needed for each stage of injection during the squeeze treatment.
Some potential drawbacks of the squeeze technology should be taken
into consideration before it is used. Firstly, squeeze lifetime is finite for a
particular volume of water production, which indicates that wells need to
be treated periodically to maintain scale control. Secondly, squeeze